3 use rustc_data_structures::fx::FxHashMap;
5 pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
9 use rustc_hir::def::{CtorKind, DefKind, Res};
10 use rustc_hir::pat_util::EnumerateAndAdjustIterator;
11 use rustc_hir::{HirId, Pat, PatKind};
12 use rustc_infer::infer;
13 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
14 use rustc_middle::middle::stability::EvalResult;
15 use rustc_middle::ty::{self, Adt, BindingMode, Ty, TypeVisitable};
16 use rustc_session::lint::builtin::NON_EXHAUSTIVE_OMITTED_PATTERNS;
17 use rustc_span::hygiene::DesugaringKind;
18 use rustc_span::lev_distance::find_best_match_for_name;
19 use rustc_span::source_map::{Span, Spanned};
20 use rustc_span::symbol::{kw, sym, Ident};
21 use rustc_span::{BytePos, DUMMY_SP};
22 use rustc_trait_selection::autoderef::Autoderef;
23 use rustc_trait_selection::traits::{ObligationCause, Pattern};
27 use std::collections::hash_map::Entry::{Occupied, Vacant};
29 use super::report_unexpected_variant_res;
31 const CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ: &str = "\
32 This error indicates that a pointer to a trait type cannot be implicitly dereferenced by a \
33 pattern. Every trait defines a type, but because the size of trait implementors isn't fixed, \
34 this type has no compile-time size. Therefore, all accesses to trait types must be through \
35 pointers. If you encounter this error you should try to avoid dereferencing the pointer.
37 You can read more about trait objects in the Trait Objects section of the Reference: \
38 https://doc.rust-lang.org/reference/types.html#trait-objects";
40 /// Information about the expected type at the top level of type checking a pattern.
42 /// **NOTE:** This is only for use by diagnostics. Do NOT use for type checking logic!
43 #[derive(Copy, Clone)]
44 struct TopInfo<'tcx> {
45 /// The `expected` type at the top level of type checking a pattern.
47 /// Was the origin of the `span` from a scrutinee expression?
49 /// Otherwise there is no scrutinee and it could be e.g. from the type of a formal parameter.
51 /// The span giving rise to the `expected` type, if one could be provided.
53 /// If `origin_expr` is `true`, then this is the span of the scrutinee as in:
55 /// - `match scrutinee { ... }`
56 /// - `let _ = scrutinee;`
58 /// This is used to point to add context in type errors.
59 /// In the following example, `span` corresponds to the `a + b` expression:
62 /// error[E0308]: mismatched types
63 /// --> src/main.rs:L:C
65 /// L | let temp: usize = match a + b {
66 /// | ----- this expression has type `usize`
67 /// L | Ok(num) => num,
68 /// | ^^^^^^^ expected `usize`, found enum `std::result::Result`
70 /// = note: expected type `usize`
71 /// found type `std::result::Result<_, _>`
76 impl<'tcx> FnCtxt<'_, 'tcx> {
77 fn pattern_cause(&self, ti: TopInfo<'tcx>, cause_span: Span) -> ObligationCause<'tcx> {
78 let code = Pattern { span: ti.span, root_ty: ti.expected, origin_expr: ti.origin_expr };
79 self.cause(cause_span, code)
82 fn demand_eqtype_pat_diag(
88 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
89 self.demand_eqtype_with_origin(&self.pattern_cause(ti, cause_span), expected, actual)
99 if let Some(mut err) = self.demand_eqtype_pat_diag(cause_span, expected, actual, ti) {
105 const INITIAL_BM: BindingMode = BindingMode::BindByValue(hir::Mutability::Not);
107 /// Mode for adjusting the expected type and binding mode.
109 /// Peel off all immediate reference types.
111 /// Reset binding mode to the initial mode.
113 /// Pass on the input binding mode and expected type.
117 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
118 /// Type check the given top level pattern against the `expected` type.
120 /// If a `Some(span)` is provided and `origin_expr` holds,
121 /// then the `span` represents the scrutinee's span.
122 /// The scrutinee is found in e.g. `match scrutinee { ... }` and `let pat = scrutinee;`.
124 /// Otherwise, `Some(span)` represents the span of a type expression
125 /// which originated the `expected` type.
126 pub fn check_pat_top(
128 pat: &'tcx Pat<'tcx>,
133 let info = TopInfo { expected, origin_expr, span };
134 self.check_pat(pat, expected, INITIAL_BM, info);
137 /// Type check the given `pat` against the `expected` type
138 /// with the provided `def_bm` (default binding mode).
140 /// Outside of this module, `check_pat_top` should always be used.
141 /// Conversely, inside this module, `check_pat_top` should never be used.
142 #[instrument(level = "debug", skip(self, ti))]
145 pat: &'tcx Pat<'tcx>,
150 let path_res = match &pat.kind {
151 PatKind::Path(qpath) => {
152 Some(self.resolve_ty_and_res_fully_qualified_call(qpath, pat.hir_id, pat.span))
156 let adjust_mode = self.calc_adjust_mode(pat, path_res.map(|(res, ..)| res));
157 let (expected, def_bm) = self.calc_default_binding_mode(pat, expected, def_bm, adjust_mode);
159 let ty = match pat.kind {
160 PatKind::Wild => expected,
161 PatKind::Lit(lt) => self.check_pat_lit(pat.span, lt, expected, ti),
162 PatKind::Range(lhs, rhs, _) => self.check_pat_range(pat.span, lhs, rhs, expected, ti),
163 PatKind::Binding(ba, var_id, _, sub) => {
164 self.check_pat_ident(pat, ba, var_id, sub, expected, def_bm, ti)
166 PatKind::TupleStruct(ref qpath, subpats, ddpos) => {
167 self.check_pat_tuple_struct(pat, qpath, subpats, ddpos, expected, def_bm, ti)
169 PatKind::Path(ref qpath) => {
170 self.check_pat_path(pat, qpath, path_res.unwrap(), expected, ti)
172 PatKind::Struct(ref qpath, fields, has_rest_pat) => {
173 self.check_pat_struct(pat, qpath, fields, has_rest_pat, expected, def_bm, ti)
175 PatKind::Or(pats) => {
177 self.check_pat(pat, expected, def_bm, ti);
181 PatKind::Tuple(elements, ddpos) => {
182 self.check_pat_tuple(pat.span, elements, ddpos, expected, def_bm, ti)
184 PatKind::Box(inner) => self.check_pat_box(pat.span, inner, expected, def_bm, ti),
185 PatKind::Ref(inner, mutbl) => {
186 self.check_pat_ref(pat, inner, mutbl, expected, def_bm, ti)
188 PatKind::Slice(before, slice, after) => {
189 self.check_pat_slice(pat.span, before, slice, after, expected, def_bm, ti)
193 self.write_ty(pat.hir_id, ty);
195 // (note_1): In most of the cases where (note_1) is referenced
196 // (literals and constants being the exception), we relate types
197 // using strict equality, even though subtyping would be sufficient.
198 // There are a few reasons for this, some of which are fairly subtle
199 // and which cost me (nmatsakis) an hour or two debugging to remember,
200 // so I thought I'd write them down this time.
202 // 1. There is no loss of expressiveness here, though it does
203 // cause some inconvenience. What we are saying is that the type
204 // of `x` becomes *exactly* what is expected. This can cause unnecessary
205 // errors in some cases, such as this one:
208 // fn foo<'x>(x: &'x i32) {
215 // The reason we might get an error is that `z` might be
216 // assigned a type like `&'x i32`, and then we would have
217 // a problem when we try to assign `&a` to `z`, because
218 // the lifetime of `&a` (i.e., the enclosing block) is
219 // shorter than `'x`.
221 // HOWEVER, this code works fine. The reason is that the
222 // expected type here is whatever type the user wrote, not
223 // the initializer's type. In this case the user wrote
224 // nothing, so we are going to create a type variable `Z`.
225 // Then we will assign the type of the initializer (`&'x i32`)
226 // as a subtype of `Z`: `&'x i32 <: Z`. And hence we
227 // will instantiate `Z` as a type `&'0 i32` where `'0` is
228 // a fresh region variable, with the constraint that `'x : '0`.
229 // So basically we're all set.
231 // Note that there are two tests to check that this remains true
232 // (`regions-reassign-{match,let}-bound-pointer.rs`).
234 // 2. Things go horribly wrong if we use subtype. The reason for
235 // THIS is a fairly subtle case involving bound regions. See the
236 // `givens` field in `region_constraints`, as well as the test
237 // `regions-relate-bound-regions-on-closures-to-inference-variables.rs`,
238 // for details. Short version is that we must sometimes detect
239 // relationships between specific region variables and regions
240 // bound in a closure signature, and that detection gets thrown
241 // off when we substitute fresh region variables here to enable
245 /// Compute the new expected type and default binding mode from the old ones
246 /// as well as the pattern form we are currently checking.
247 fn calc_default_binding_mode(
249 pat: &'tcx Pat<'tcx>,
252 adjust_mode: AdjustMode,
253 ) -> (Ty<'tcx>, BindingMode) {
255 AdjustMode::Pass => (expected, def_bm),
256 AdjustMode::Reset => (expected, INITIAL_BM),
257 AdjustMode::Peel => self.peel_off_references(pat, expected, def_bm),
261 /// How should the binding mode and expected type be adjusted?
263 /// When the pattern is a path pattern, `opt_path_res` must be `Some(res)`.
264 fn calc_adjust_mode(&self, pat: &'tcx Pat<'tcx>, opt_path_res: Option<Res>) -> AdjustMode {
265 // When we perform destructuring assignment, we disable default match bindings, which are
266 // unintuitive in this context.
267 if !pat.default_binding_modes {
268 return AdjustMode::Reset;
271 // Type checking these product-like types successfully always require
272 // that the expected type be of those types and not reference types.
274 | PatKind::TupleStruct(..)
278 | PatKind::Slice(..) => AdjustMode::Peel,
279 // String and byte-string literals result in types `&str` and `&[u8]` respectively.
280 // All other literals result in non-reference types.
281 // As a result, we allow `if let 0 = &&0 {}` but not `if let "foo" = &&"foo {}`.
283 // Call `resolve_vars_if_possible` here for inline const blocks.
284 PatKind::Lit(lt) => match self.resolve_vars_if_possible(self.check_expr(lt)).kind() {
285 ty::Ref(..) => AdjustMode::Pass,
286 _ => AdjustMode::Peel,
288 PatKind::Path(_) => match opt_path_res.unwrap() {
289 // These constants can be of a reference type, e.g. `const X: &u8 = &0;`.
290 // Peeling the reference types too early will cause type checking failures.
291 // Although it would be possible to *also* peel the types of the constants too.
292 Res::Def(DefKind::Const | DefKind::AssocConst, _) => AdjustMode::Pass,
293 // In the `ValueNS`, we have `SelfCtor(..) | Ctor(_, Const), _)` remaining which
294 // could successfully compile. The former being `Self` requires a unit struct.
295 // In either case, and unlike constants, the pattern itself cannot be
296 // a reference type wherefore peeling doesn't give up any expressiveness.
297 _ => AdjustMode::Peel,
299 // When encountering a `& mut? pat` pattern, reset to "by value".
300 // This is so that `x` and `y` here are by value, as they appear to be:
303 // match &(&22, &44) {
309 PatKind::Ref(..) => AdjustMode::Reset,
310 // A `_` pattern works with any expected type, so there's no need to do anything.
312 // Bindings also work with whatever the expected type is,
313 // and moreover if we peel references off, that will give us the wrong binding type.
314 // Also, we can have a subpattern `binding @ pat`.
315 // Each side of the `@` should be treated independently (like with OR-patterns).
316 | PatKind::Binding(..)
317 // An OR-pattern just propagates to each individual alternative.
318 // This is maximally flexible, allowing e.g., `Some(mut x) | &Some(mut x)`.
319 // In that example, `Some(mut x)` results in `Peel` whereas `&Some(mut x)` in `Reset`.
320 | PatKind::Or(_) => AdjustMode::Pass,
324 /// Peel off as many immediately nested `& mut?` from the expected type as possible
325 /// and return the new expected type and binding default binding mode.
326 /// The adjustments vector, if non-empty is stored in a table.
327 fn peel_off_references(
329 pat: &'tcx Pat<'tcx>,
331 mut def_bm: BindingMode,
332 ) -> (Ty<'tcx>, BindingMode) {
333 let mut expected = self.resolve_vars_with_obligations(expected);
335 // Peel off as many `&` or `&mut` from the scrutinee type as possible. For example,
336 // for `match &&&mut Some(5)` the loop runs three times, aborting when it reaches
337 // the `Some(5)` which is not of type Ref.
339 // For each ampersand peeled off, update the binding mode and push the original
340 // type into the adjustments vector.
342 // See the examples in `ui/match-defbm*.rs`.
343 let mut pat_adjustments = vec![];
344 while let ty::Ref(_, inner_ty, inner_mutability) = *expected.kind() {
345 debug!("inspecting {:?}", expected);
347 debug!("current discriminant is Ref, inserting implicit deref");
348 // Preserve the reference type. We'll need it later during THIR lowering.
349 pat_adjustments.push(expected);
352 def_bm = ty::BindByReference(match def_bm {
353 // If default binding mode is by value, make it `ref` or `ref mut`
354 // (depending on whether we observe `&` or `&mut`).
356 // When `ref mut`, stay a `ref mut` (on `&mut`) or downgrade to `ref` (on `&`).
357 ty::BindByReference(hir::Mutability::Mut) => inner_mutability,
358 // Once a `ref`, always a `ref`.
359 // This is because a `& &mut` cannot mutate the underlying value.
360 ty::BindByReference(m @ hir::Mutability::Not) => m,
364 if !pat_adjustments.is_empty() {
365 debug!("default binding mode is now {:?}", def_bm);
369 .pat_adjustments_mut()
370 .insert(pat.hir_id, pat_adjustments);
379 lt: &hir::Expr<'tcx>,
383 // We've already computed the type above (when checking for a non-ref pat),
384 // so avoid computing it again.
385 let ty = self.node_ty(lt.hir_id);
387 // Byte string patterns behave the same way as array patterns
388 // They can denote both statically and dynamically-sized byte arrays.
390 if let hir::ExprKind::Lit(Spanned { node: ast::LitKind::ByteStr(_), .. }) = lt.kind {
391 let expected = self.structurally_resolved_type(span, expected);
392 if let ty::Ref(_, inner_ty, _) = expected.kind()
393 && matches!(inner_ty.kind(), ty::Slice(_))
396 trace!(?lt.hir_id.local_id, "polymorphic byte string lit");
399 .treat_byte_string_as_slice
400 .insert(lt.hir_id.local_id);
401 pat_ty = tcx.mk_imm_ref(tcx.lifetimes.re_static, tcx.mk_slice(tcx.types.u8));
405 // Somewhat surprising: in this case, the subtyping relation goes the
406 // opposite way as the other cases. Actually what we really want is not
407 // a subtyping relation at all but rather that there exists a LUB
408 // (so that they can be compared). However, in practice, constants are
409 // always scalars or strings. For scalars subtyping is irrelevant,
410 // and for strings `ty` is type is `&'static str`, so if we say that
412 // &'static str <: expected
414 // then that's equivalent to there existing a LUB.
415 let cause = self.pattern_cause(ti, span);
416 if let Some(mut err) = self.demand_suptype_with_origin(&cause, expected, pat_ty) {
420 // In the case of `if`- and `while`-expressions we've already checked
421 // that `scrutinee: bool`. We know that the pattern is `true`,
422 // so an error here would be a duplicate and from the wrong POV.
423 s.is_desugaring(DesugaringKind::CondTemporary)
435 lhs: Option<&'tcx hir::Expr<'tcx>>,
436 rhs: Option<&'tcx hir::Expr<'tcx>>,
440 let calc_side = |opt_expr: Option<&'tcx hir::Expr<'tcx>>| match opt_expr {
443 let ty = self.check_expr(expr);
444 // Check that the end-point is possibly of numeric or char type.
445 // The early check here is not for correctness, but rather better
446 // diagnostics (e.g. when `&str` is being matched, `expected` will
447 // be peeled to `str` while ty here is still `&str`, if we don't
448 // err early here, a rather confusing unification error will be
451 !(ty.is_numeric() || ty.is_char() || ty.is_ty_var() || ty.references_error());
452 Some((fail, ty, expr.span))
455 let mut lhs = calc_side(lhs);
456 let mut rhs = calc_side(rhs);
458 if let (Some((true, ..)), _) | (_, Some((true, ..))) = (lhs, rhs) {
459 // There exists a side that didn't meet our criteria that the end-point
460 // be of a numeric or char type, as checked in `calc_side` above.
461 self.emit_err_pat_range(span, lhs, rhs);
462 return self.tcx.ty_error();
465 // Unify each side with `expected`.
466 // Subtyping doesn't matter here, as the value is some kind of scalar.
467 let demand_eqtype = |x: &mut _, y| {
468 if let Some((ref mut fail, x_ty, x_span)) = *x
469 && let Some(mut err) = self.demand_eqtype_pat_diag(x_span, expected, x_ty, ti)
471 if let Some((_, y_ty, y_span)) = y {
472 self.endpoint_has_type(&mut err, y_span, y_ty);
478 demand_eqtype(&mut lhs, rhs);
479 demand_eqtype(&mut rhs, lhs);
481 if let (Some((true, ..)), _) | (_, Some((true, ..))) = (lhs, rhs) {
482 return self.tcx.ty_error();
485 // Find the unified type and check if it's of numeric or char type again.
486 // This check is needed if both sides are inference variables.
487 // We require types to be resolved here so that we emit inference failure
488 // rather than "_ is not a char or numeric".
489 let ty = self.structurally_resolved_type(span, expected);
490 if !(ty.is_numeric() || ty.is_char() || ty.references_error()) {
491 if let Some((ref mut fail, _, _)) = lhs {
494 if let Some((ref mut fail, _, _)) = rhs {
497 self.emit_err_pat_range(span, lhs, rhs);
498 return self.tcx.ty_error();
503 fn endpoint_has_type(&self, err: &mut Diagnostic, span: Span, ty: Ty<'_>) {
504 if !ty.references_error() {
505 err.span_label(span, &format!("this is of type `{}`", ty));
509 fn emit_err_pat_range(
512 lhs: Option<(bool, Ty<'tcx>, Span)>,
513 rhs: Option<(bool, Ty<'tcx>, Span)>,
515 let span = match (lhs, rhs) {
516 (Some((true, ..)), Some((true, ..))) => span,
517 (Some((true, _, sp)), _) => sp,
518 (_, Some((true, _, sp))) => sp,
519 _ => span_bug!(span, "emit_err_pat_range: no side failed or exists but still error?"),
521 let mut err = struct_span_err!(
525 "only `char` and numeric types are allowed in range patterns"
528 let ty = self.resolve_vars_if_possible(ty);
529 format!("this is of type `{}` but it should be `char` or numeric", ty)
531 let mut one_side_err = |first_span, first_ty, second: Option<(bool, Ty<'tcx>, Span)>| {
532 err.span_label(first_span, &msg(first_ty));
533 if let Some((_, ty, sp)) = second {
534 let ty = self.resolve_vars_if_possible(ty);
535 self.endpoint_has_type(&mut err, sp, ty);
539 (Some((true, lhs_ty, lhs_sp)), Some((true, rhs_ty, rhs_sp))) => {
540 err.span_label(lhs_sp, &msg(lhs_ty));
541 err.span_label(rhs_sp, &msg(rhs_ty));
543 (Some((true, lhs_ty, lhs_sp)), rhs) => one_side_err(lhs_sp, lhs_ty, rhs),
544 (lhs, Some((true, rhs_ty, rhs_sp))) => one_side_err(rhs_sp, rhs_ty, lhs),
545 _ => span_bug!(span, "Impossible, verified above."),
547 if self.tcx.sess.teach(&err.get_code().unwrap()) {
549 "In a match expression, only numbers and characters can be matched \
550 against a range. This is because the compiler checks that the range \
551 is non-empty at compile-time, and is unable to evaluate arbitrary \
552 comparison functions. If you want to capture values of an orderable \
553 type between two end-points, you can use a guard.",
561 pat: &'tcx Pat<'tcx>,
562 ba: hir::BindingAnnotation,
564 sub: Option<&'tcx Pat<'tcx>>,
569 // Determine the binding mode...
571 hir::BindingAnnotation::NONE => def_bm,
572 _ => BindingMode::convert(ba),
574 // ...and store it in a side table:
575 self.inh.typeck_results.borrow_mut().pat_binding_modes_mut().insert(pat.hir_id, bm);
577 debug!("check_pat_ident: pat.hir_id={:?} bm={:?}", pat.hir_id, bm);
579 let local_ty = self.local_ty(pat.span, pat.hir_id).decl_ty;
580 let eq_ty = match bm {
581 ty::BindByReference(mutbl) => {
582 // If the binding is like `ref x | ref mut x`,
583 // then `x` is assigned a value of type `&M T` where M is the
584 // mutability and T is the expected type.
586 // `x` is assigned a value of type `&M T`, hence `&M T <: typeof(x)`
587 // is required. However, we use equality, which is stronger.
588 // See (note_1) for an explanation.
589 self.new_ref_ty(pat.span, mutbl, expected)
591 // Otherwise, the type of x is the expected type `T`.
592 ty::BindByValue(_) => {
593 // As above, `T <: typeof(x)` is required, but we use equality, see (note_1).
597 self.demand_eqtype_pat(pat.span, eq_ty, local_ty, ti);
599 // If there are multiple arms, make sure they all agree on
600 // what the type of the binding `x` ought to be.
601 if var_id != pat.hir_id {
602 self.check_binding_alt_eq_ty(ba, pat.span, var_id, local_ty, ti);
605 if let Some(p) = sub {
606 self.check_pat(p, expected, def_bm, ti);
612 fn check_binding_alt_eq_ty(
614 ba: hir::BindingAnnotation,
620 let var_ty = self.local_ty(span, var_id).decl_ty;
621 if let Some(mut err) = self.demand_eqtype_pat_diag(span, var_ty, ty, ti) {
622 let hir = self.tcx.hir();
623 let var_ty = self.resolve_vars_with_obligations(var_ty);
624 let msg = format!("first introduced with type `{var_ty}` here");
625 err.span_label(hir.span(var_id), msg);
626 let in_match = hir.parent_iter(var_id).any(|(_, n)| {
629 hir::Node::Expr(hir::Expr {
630 kind: hir::ExprKind::Match(.., hir::MatchSource::Normal),
635 let pre = if in_match { "in the same arm, " } else { "" };
636 err.note(&format!("{}a binding must have the same type in all alternatives", pre));
637 self.suggest_adding_missing_ref_or_removing_ref(
641 self.resolve_vars_with_obligations(ty),
648 fn suggest_adding_missing_ref_or_removing_ref(
650 err: &mut Diagnostic,
654 ba: hir::BindingAnnotation,
656 match (expected.kind(), actual.kind(), ba) {
657 (ty::Ref(_, inner_ty, _), _, hir::BindingAnnotation::NONE)
658 if self.can_eq(self.param_env, *inner_ty, actual).is_ok() =>
660 err.span_suggestion_verbose(
662 "consider adding `ref`",
664 Applicability::MaybeIncorrect,
667 (_, ty::Ref(_, inner_ty, _), hir::BindingAnnotation::REF)
668 if self.can_eq(self.param_env, expected, *inner_ty).is_ok() =>
670 err.span_suggestion_verbose(
671 span.with_hi(span.lo() + BytePos(4)),
672 "consider removing `ref`",
674 Applicability::MaybeIncorrect,
681 // Precondition: pat is a Ref(_) pattern
682 fn borrow_pat_suggestion(&self, err: &mut Diagnostic, pat: &Pat<'_>) {
684 if let PatKind::Ref(inner, mutbl) = pat.kind
685 && let PatKind::Binding(_, _, binding, ..) = inner.kind {
686 let binding_parent_id = tcx.hir().get_parent_node(pat.hir_id);
687 let binding_parent = tcx.hir().get(binding_parent_id);
688 debug!(?inner, ?pat, ?binding_parent);
690 let mutability = match mutbl {
691 ast::Mutability::Mut => "mut",
692 ast::Mutability::Not => "",
695 let mut_var_suggestion = 'block: {
696 if !matches!(mutbl, ast::Mutability::Mut) {
700 let ident_kind = match binding_parent {
701 hir::Node::Param(_) => "parameter",
702 hir::Node::Local(_) => "variable",
703 hir::Node::Arm(_) => "binding",
705 // Provide diagnostics only if the parent pattern is struct-like,
706 // i.e. where `mut binding` makes sense
707 hir::Node::Pat(Pat { kind, .. }) => match kind {
709 | PatKind::TupleStruct(..)
712 | PatKind::Slice(..) => "binding",
715 | PatKind::Binding(..)
720 | PatKind::Range(..) => break 'block None,
723 // Don't provide suggestions in other cases
724 _ => break 'block None,
729 format!("to declare a mutable {ident_kind} use"),
730 format!("mut {binding}"),
735 match binding_parent {
736 // Check that there is explicit type (ie this is not a closure param with inferred type)
737 // so we don't suggest moving something to the type that does not exist
738 hir::Node::Param(hir::Param { ty_span, .. }) if binding.span != *ty_span => {
739 err.multipart_suggestion_verbose(
740 format!("to take parameter `{binding}` by reference, move `&{mutability}` to the type"),
742 (pat.span.until(inner.span), "".to_owned()),
743 (ty_span.shrink_to_lo(), format!("&{}", mutbl.prefix_str())),
745 Applicability::MachineApplicable
748 if let Some((sp, msg, sugg)) = mut_var_suggestion {
749 err.span_note(sp, format!("{msg}: `{sugg}`"));
752 hir::Node::Param(_) | hir::Node::Arm(_) | hir::Node::Pat(_) => {
753 // rely on match ergonomics or it might be nested `&&pat`
754 err.span_suggestion_verbose(
755 pat.span.until(inner.span),
756 format!("consider removing `&{mutability}` from the pattern"),
758 Applicability::MaybeIncorrect,
761 if let Some((sp, msg, sugg)) = mut_var_suggestion {
762 err.span_note(sp, format!("{msg}: `{sugg}`"));
765 _ if let Some((sp, msg, sugg)) = mut_var_suggestion => {
766 err.span_suggestion(sp, msg, sugg, Applicability::MachineApplicable);
768 _ => {} // don't provide suggestions in other cases #55175
773 pub fn check_dereferenceable(&self, span: Span, expected: Ty<'tcx>, inner: &Pat<'_>) -> bool {
774 if let PatKind::Binding(..) = inner.kind
775 && let Some(mt) = self.shallow_resolve(expected).builtin_deref(true)
776 && let ty::Dynamic(..) = mt.ty.kind()
778 // This is "x = SomeTrait" being reduced from
779 // "let &x = &SomeTrait" or "let box x = Box<SomeTrait>", an error.
780 let type_str = self.ty_to_string(expected);
781 let mut err = struct_span_err!(
785 "type `{}` cannot be dereferenced",
788 err.span_label(span, format!("type `{type_str}` cannot be dereferenced"));
789 if self.tcx.sess.teach(&err.get_code().unwrap()) {
790 err.note(CANNOT_IMPLICITLY_DEREF_POINTER_TRAIT_OBJ);
800 pat: &'tcx Pat<'tcx>,
801 qpath: &hir::QPath<'_>,
802 fields: &'tcx [hir::PatField<'tcx>],
808 // Resolve the path and check the definition for errors.
809 let Some((variant, pat_ty)) = self.check_struct_path(qpath, pat.hir_id) else {
810 let err = self.tcx.ty_error();
811 for field in fields {
813 self.check_pat(field.pat, err, def_bm, ti);
818 // Type-check the path.
819 self.demand_eqtype_pat(pat.span, expected, pat_ty, ti);
821 // Type-check subpatterns.
822 if self.check_struct_pat_fields(pat_ty, &pat, variant, fields, has_rest_pat, def_bm, ti) {
832 qpath: &hir::QPath<'_>,
833 path_resolution: (Res, Option<Ty<'tcx>>, &'tcx [hir::PathSegment<'tcx>]),
839 // We have already resolved the path.
840 let (res, opt_ty, segments) = path_resolution;
843 self.set_tainted_by_errors();
844 return tcx.ty_error();
846 Res::Def(DefKind::AssocFn | DefKind::Ctor(_, CtorKind::Fictive | CtorKind::Fn), _) => {
847 report_unexpected_variant_res(tcx, res, qpath, pat.span);
848 return tcx.ty_error();
852 DefKind::Ctor(_, CtorKind::Const)
854 | DefKind::AssocConst
855 | DefKind::ConstParam,
858 _ => bug!("unexpected pattern resolution: {:?}", res),
861 // Type-check the path.
862 let (pat_ty, pat_res) =
863 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
865 self.demand_suptype_with_origin(&self.pattern_cause(ti, pat.span), expected, pat_ty)
867 self.emit_bad_pat_path(err, pat, res, pat_res, pat_ty, segments);
872 fn maybe_suggest_range_literal(
875 opt_def_id: Option<hir::def_id::DefId>,
879 Some(def_id) => match self.tcx.hir().get_if_local(def_id) {
880 Some(hir::Node::Item(hir::Item {
881 kind: hir::ItemKind::Const(_, body_id), ..
882 })) => match self.tcx.hir().get(body_id.hir_id) {
883 hir::Node::Expr(expr) => {
884 if hir::is_range_literal(expr) {
885 let span = self.tcx.hir().span(body_id.hir_id);
886 if let Ok(snip) = self.tcx.sess.source_map().span_to_snippet(span) {
887 e.span_suggestion_verbose(
889 "you may want to move the range into the match block",
891 Applicability::MachineApplicable,
906 fn emit_bad_pat_path(
908 mut e: DiagnosticBuilder<'_, ErrorGuaranteed>,
909 pat: &hir::Pat<'tcx>,
913 segments: &'tcx [hir::PathSegment<'tcx>],
915 let pat_span = pat.span;
916 if let Some(span) = self.tcx.hir().res_span(pat_res) {
917 e.span_label(span, &format!("{} defined here", res.descr()));
918 if let [hir::PathSegment { ident, .. }] = &*segments {
922 "`{}` is interpreted as {} {}, not a new binding",
928 match self.tcx.hir().get(self.tcx.hir().get_parent_node(pat.hir_id)) {
929 hir::Node::PatField(..) => {
930 e.span_suggestion_verbose(
931 ident.span.shrink_to_hi(),
932 "bind the struct field to a different name instead",
933 format!(": other_{}", ident.as_str().to_lowercase()),
934 Applicability::HasPlaceholders,
938 let (type_def_id, item_def_id) = match pat_ty.kind() {
939 Adt(def, _) => match res {
940 Res::Def(DefKind::Const, def_id) => (Some(def.did()), Some(def_id)),
947 self.tcx.lang_items().range_struct(),
948 self.tcx.lang_items().range_from_struct(),
949 self.tcx.lang_items().range_to_struct(),
950 self.tcx.lang_items().range_full_struct(),
951 self.tcx.lang_items().range_inclusive_struct(),
952 self.tcx.lang_items().range_to_inclusive_struct(),
954 if type_def_id != None && ranges.contains(&type_def_id) {
955 if !self.maybe_suggest_range_literal(&mut e, item_def_id, *ident) {
956 let msg = "constants only support matching by type, \
957 if you meant to match against a range of values, \
958 consider using a range pattern like `min ..= max` in the match block";
962 let msg = "introduce a new binding instead";
963 let sugg = format!("other_{}", ident.as_str().to_lowercase());
968 Applicability::HasPlaceholders,
978 fn check_pat_tuple_struct(
980 pat: &'tcx Pat<'tcx>,
981 qpath: &'tcx hir::QPath<'tcx>,
982 subpats: &'tcx [Pat<'tcx>],
983 ddpos: hir::DotDotPos,
991 self.check_pat(pat, tcx.ty_error(), def_bm, ti);
994 let report_unexpected_res = |res: Res| {
995 let sm = tcx.sess.source_map();
997 .span_to_snippet(sm.span_until_char(pat.span, '('))
998 .map_or_else(|_| String::new(), |s| format!(" `{}`", s.trim_end()));
1000 "expected tuple struct or tuple variant, found {}{}",
1005 let mut err = struct_span_err!(tcx.sess, pat.span, E0164, "{msg}");
1007 Res::Def(DefKind::Fn | DefKind::AssocFn, _) => {
1008 err.span_label(pat.span, "`fn` calls are not allowed in patterns");
1010 "for more information, visit \
1011 https://doc.rust-lang.org/book/ch18-00-patterns.html",
1015 err.span_label(pat.span, "not a tuple variant or struct");
1022 // Resolve the path and check the definition for errors.
1023 let (res, opt_ty, segments) =
1024 self.resolve_ty_and_res_fully_qualified_call(qpath, pat.hir_id, pat.span);
1025 if res == Res::Err {
1026 self.set_tainted_by_errors();
1028 return self.tcx.ty_error();
1031 // Type-check the path.
1033 self.instantiate_value_path(segments, opt_ty, res, pat.span, pat.hir_id);
1034 if !pat_ty.is_fn() {
1035 report_unexpected_res(res);
1036 return tcx.ty_error();
1039 let variant = match res {
1041 self.set_tainted_by_errors();
1043 return tcx.ty_error();
1045 Res::Def(DefKind::AssocConst | DefKind::AssocFn, _) => {
1046 report_unexpected_res(res);
1047 return tcx.ty_error();
1049 Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) => tcx.expect_variant_res(res),
1050 _ => bug!("unexpected pattern resolution: {:?}", res),
1053 // Replace constructor type with constructed type for tuple struct patterns.
1054 let pat_ty = pat_ty.fn_sig(tcx).output();
1055 let pat_ty = pat_ty.no_bound_vars().expect("expected fn type");
1057 // Type-check the tuple struct pattern against the expected type.
1058 let diag = self.demand_eqtype_pat_diag(pat.span, expected, pat_ty, ti);
1059 let had_err = if let Some(mut err) = diag {
1066 // Type-check subpatterns.
1067 if subpats.len() == variant.fields.len()
1068 || subpats.len() < variant.fields.len() && ddpos.as_opt_usize().is_some()
1070 let ty::Adt(_, substs) = pat_ty.kind() else {
1071 bug!("unexpected pattern type {:?}", pat_ty);
1073 for (i, subpat) in subpats.iter().enumerate_and_adjust(variant.fields.len(), ddpos) {
1074 let field_ty = self.field_ty(subpat.span, &variant.fields[i], substs);
1075 self.check_pat(subpat, field_ty, def_bm, ti);
1077 self.tcx.check_stability(
1078 variant.fields[i].did,
1085 // Pattern has wrong number of fields.
1086 self.e0023(pat.span, res, qpath, subpats, &variant.fields, expected, had_err);
1088 return tcx.ty_error();
1097 qpath: &hir::QPath<'_>,
1098 subpats: &'tcx [Pat<'tcx>],
1099 fields: &'tcx [ty::FieldDef],
1103 let subpats_ending = pluralize!(subpats.len());
1104 let fields_ending = pluralize!(fields.len());
1106 let subpat_spans = if subpats.is_empty() {
1109 subpats.iter().map(|p| p.span).collect()
1111 let last_subpat_span = *subpat_spans.last().unwrap();
1112 let res_span = self.tcx.def_span(res.def_id());
1113 let def_ident_span = self.tcx.def_ident_span(res.def_id()).unwrap_or(res_span);
1114 let field_def_spans = if fields.is_empty() {
1117 fields.iter().map(|f| f.ident(self.tcx).span).collect()
1119 let last_field_def_span = *field_def_spans.last().unwrap();
1121 let mut err = struct_span_err!(
1123 MultiSpan::from_spans(subpat_spans),
1125 "this pattern has {} field{}, but the corresponding {} has {} field{}",
1134 &format!("expected {} field{}, found {}", fields.len(), fields_ending, subpats.len()),
1136 if self.tcx.sess.source_map().is_multiline(qpath.span().between(last_subpat_span)) {
1137 err.span_label(qpath.span(), "");
1139 if self.tcx.sess.source_map().is_multiline(def_ident_span.between(last_field_def_span)) {
1140 err.span_label(def_ident_span, format!("{} defined here", res.descr()));
1142 for span in &field_def_spans[..field_def_spans.len() - 1] {
1143 err.span_label(*span, "");
1146 last_field_def_span,
1147 &format!("{} has {} field{}", res.descr(), fields.len(), fields_ending),
1150 // Identify the case `Some(x, y)` where the expected type is e.g. `Option<(T, U)>`.
1151 // More generally, the expected type wants a tuple variant with one field of an
1152 // N-arity-tuple, e.g., `V_i((p_0, .., p_N))`. Meanwhile, the user supplied a pattern
1153 // with the subpatterns directly in the tuple variant pattern, e.g., `V_i(p_0, .., p_N)`.
1154 let missing_parentheses = match (&expected.kind(), fields, had_err) {
1155 // #67037: only do this if we could successfully type-check the expected type against
1156 // the tuple struct pattern. Otherwise the substs could get out of range on e.g.,
1157 // `let P() = U;` where `P != U` with `struct P<T>(T);`.
1158 (ty::Adt(_, substs), [field], false) => {
1159 let field_ty = self.field_ty(pat_span, field, substs);
1160 match field_ty.kind() {
1161 ty::Tuple(fields) => fields.len() == subpats.len(),
1167 if missing_parentheses {
1168 let (left, right) = match subpats {
1169 // This is the zero case; we aim to get the "hi" part of the `QPath`'s
1170 // span as the "lo" and then the "hi" part of the pattern's span as the "hi".
1173 // help: missing parentheses
1175 // L | let A(()) = A(());
1177 [] => (qpath.span().shrink_to_hi(), pat_span),
1178 // Easy case. Just take the "lo" of the first sub-pattern and the "hi" of the
1179 // last sub-pattern. In the case of `A(x)` the first and last may coincide.
1182 // help: missing parentheses
1184 // L | let A((x, y)) = A((1, 2));
1186 [first, ..] => (first.span.shrink_to_lo(), subpats.last().unwrap().span),
1188 err.multipart_suggestion(
1189 "missing parentheses",
1190 vec![(left, "(".to_string()), (right.shrink_to_hi(), ")".to_string())],
1191 Applicability::MachineApplicable,
1193 } else if fields.len() > subpats.len() && pat_span != DUMMY_SP {
1194 let after_fields_span = pat_span.with_hi(pat_span.hi() - BytePos(1)).shrink_to_hi();
1195 let all_fields_span = match subpats {
1196 [] => after_fields_span,
1197 [field] => field.span,
1198 [first, .., last] => first.span.to(last.span),
1201 // Check if all the fields in the pattern are wildcards.
1202 let all_wildcards = subpats.iter().all(|pat| matches!(pat.kind, PatKind::Wild));
1203 let first_tail_wildcard =
1204 subpats.iter().enumerate().fold(None, |acc, (pos, pat)| match (acc, &pat.kind) {
1205 (None, PatKind::Wild) => Some(pos),
1206 (Some(_), PatKind::Wild) => acc,
1209 let tail_span = match first_tail_wildcard {
1210 None => after_fields_span,
1211 Some(0) => subpats[0].span.to(after_fields_span),
1212 Some(pos) => subpats[pos - 1].span.shrink_to_hi().to(after_fields_span),
1215 // FIXME: heuristic-based suggestion to check current types for where to add `_`.
1216 let mut wildcard_sugg = vec!["_"; fields.len() - subpats.len()].join(", ");
1217 if !subpats.is_empty() {
1218 wildcard_sugg = String::from(", ") + &wildcard_sugg;
1221 err.span_suggestion_verbose(
1223 "use `_` to explicitly ignore each field",
1225 Applicability::MaybeIncorrect,
1228 // Only suggest `..` if more than one field is missing
1229 // or the pattern consists of all wildcards.
1230 if fields.len() - subpats.len() > 1 || all_wildcards {
1231 if subpats.is_empty() || all_wildcards {
1232 err.span_suggestion_verbose(
1234 "use `..` to ignore all fields",
1236 Applicability::MaybeIncorrect,
1239 err.span_suggestion_verbose(
1241 "use `..` to ignore the rest of the fields",
1243 Applicability::MaybeIncorrect,
1255 elements: &'tcx [Pat<'tcx>],
1256 ddpos: hir::DotDotPos,
1258 def_bm: BindingMode,
1262 let mut expected_len = elements.len();
1263 if ddpos.as_opt_usize().is_some() {
1264 // Require known type only when `..` is present.
1265 if let ty::Tuple(tys) = self.structurally_resolved_type(span, expected).kind() {
1266 expected_len = tys.len();
1269 let max_len = cmp::max(expected_len, elements.len());
1271 let element_tys_iter = (0..max_len).map(|_| {
1273 // FIXME: `MiscVariable` for now -- obtaining the span and name information
1274 // from all tuple elements isn't trivial.
1275 TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span },
1278 let element_tys = tcx.mk_type_list(element_tys_iter);
1279 let pat_ty = tcx.mk_ty(ty::Tuple(element_tys));
1280 if let Some(mut err) = self.demand_eqtype_pat_diag(span, expected, pat_ty, ti) {
1282 // Walk subpatterns with an expected type of `err` in this case to silence
1283 // further errors being emitted when using the bindings. #50333
1284 let element_tys_iter = (0..max_len).map(|_| tcx.ty_error());
1285 for (_, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
1286 self.check_pat(elem, tcx.ty_error(), def_bm, ti);
1288 tcx.mk_tup(element_tys_iter)
1290 for (i, elem) in elements.iter().enumerate_and_adjust(max_len, ddpos) {
1291 self.check_pat(elem, element_tys[i], def_bm, ti);
1297 fn check_struct_pat_fields(
1300 pat: &'tcx Pat<'tcx>,
1301 variant: &'tcx ty::VariantDef,
1302 fields: &'tcx [hir::PatField<'tcx>],
1304 def_bm: BindingMode,
1309 let ty::Adt(adt, substs) = adt_ty.kind() else {
1310 span_bug!(pat.span, "struct pattern is not an ADT");
1313 // Index the struct fields' types.
1314 let field_map = variant
1318 .map(|(i, field)| (field.ident(self.tcx).normalize_to_macros_2_0(), (i, field)))
1319 .collect::<FxHashMap<_, _>>();
1321 // Keep track of which fields have already appeared in the pattern.
1322 let mut used_fields = FxHashMap::default();
1323 let mut no_field_errors = true;
1325 let mut inexistent_fields = vec![];
1326 // Typecheck each field.
1327 for field in fields {
1328 let span = field.span;
1329 let ident = tcx.adjust_ident(field.ident, variant.def_id);
1330 let field_ty = match used_fields.entry(ident) {
1331 Occupied(occupied) => {
1332 self.error_field_already_bound(span, field.ident, *occupied.get());
1333 no_field_errors = false;
1337 vacant.insert(span);
1341 self.write_field_index(field.hir_id, *i);
1342 self.tcx.check_stability(f.did, Some(pat.hir_id), span, None);
1343 self.field_ty(span, f, substs)
1345 .unwrap_or_else(|| {
1346 inexistent_fields.push(field);
1347 no_field_errors = false;
1353 self.check_pat(field.pat, field_ty, def_bm, ti);
1356 let mut unmentioned_fields = variant
1359 .map(|field| (field, field.ident(self.tcx).normalize_to_macros_2_0()))
1360 .filter(|(_, ident)| !used_fields.contains_key(ident))
1361 .collect::<Vec<_>>();
1363 let inexistent_fields_err = if !(inexistent_fields.is_empty() || variant.is_recovered())
1364 && !inexistent_fields.iter().any(|field| field.ident.name == kw::Underscore)
1366 Some(self.error_inexistent_fields(
1367 adt.variant_descr(),
1369 &mut unmentioned_fields,
1377 // Require `..` if struct has non_exhaustive attribute.
1378 let non_exhaustive = variant.is_field_list_non_exhaustive() && !adt.did().is_local();
1379 if non_exhaustive && !has_rest_pat {
1380 self.error_foreign_non_exhaustive_spat(pat, adt.variant_descr(), fields.is_empty());
1383 let mut unmentioned_err = None;
1384 // Report an error if an incorrect number of fields was specified.
1386 if fields.len() != 1 {
1388 .struct_span_err(pat.span, "union patterns should have exactly one field")
1392 tcx.sess.struct_span_err(pat.span, "`..` cannot be used in union patterns").emit();
1394 } else if !unmentioned_fields.is_empty() {
1395 let accessible_unmentioned_fields: Vec<_> = unmentioned_fields
1398 .filter(|(field, _)| {
1399 field.vis.is_accessible_from(tcx.parent_module(pat.hir_id), tcx)
1401 tcx.eval_stability(field.did, None, DUMMY_SP, None),
1402 EvalResult::Deny { .. }
1404 // We only want to report the error if it is hidden and not local
1405 && !(tcx.is_doc_hidden(field.did) && !field.did.is_local())
1410 if accessible_unmentioned_fields.is_empty() {
1411 unmentioned_err = Some(self.error_no_accessible_fields(pat, fields));
1413 unmentioned_err = Some(self.error_unmentioned_fields(
1415 &accessible_unmentioned_fields,
1416 accessible_unmentioned_fields.len() != unmentioned_fields.len(),
1420 } else if non_exhaustive && !accessible_unmentioned_fields.is_empty() {
1421 self.lint_non_exhaustive_omitted_patterns(
1423 &accessible_unmentioned_fields,
1428 match (inexistent_fields_err, unmentioned_err) {
1429 (Some(mut i), Some(mut u)) => {
1430 if let Some(mut e) = self.error_tuple_variant_as_struct_pat(pat, fields, variant) {
1431 // We don't want to show the nonexistent fields error when this was
1432 // `Foo { a, b }` when it should have been `Foo(a, b)`.
1441 (None, Some(mut u)) => {
1442 if let Some(mut e) = self.error_tuple_variant_as_struct_pat(pat, fields, variant) {
1449 (Some(mut err), None) => {
1452 (None, None) if let Some(mut err) =
1453 self.error_tuple_variant_index_shorthand(variant, pat, fields) =>
1462 fn error_tuple_variant_index_shorthand(
1464 variant: &VariantDef,
1466 fields: &[hir::PatField<'_>],
1467 ) -> Option<DiagnosticBuilder<'_, ErrorGuaranteed>> {
1468 // if this is a tuple struct, then all field names will be numbers
1469 // so if any fields in a struct pattern use shorthand syntax, they will
1470 // be invalid identifiers (for example, Foo { 0, 1 }).
1471 if let (CtorKind::Fn, PatKind::Struct(qpath, field_patterns, ..)) =
1472 (variant.ctor_kind, &pat.kind)
1474 let has_shorthand_field_name = field_patterns.iter().any(|field| field.is_shorthand);
1475 if has_shorthand_field_name {
1476 let path = rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1477 s.print_qpath(qpath, false)
1479 let mut err = struct_span_err!(
1483 "tuple variant `{path}` written as struct variant",
1485 err.span_suggestion_verbose(
1486 qpath.span().shrink_to_hi().to(pat.span.shrink_to_hi()),
1487 "use the tuple variant pattern syntax instead",
1488 format!("({})", self.get_suggested_tuple_struct_pattern(fields, variant)),
1489 Applicability::MaybeIncorrect,
1497 fn error_foreign_non_exhaustive_spat(&self, pat: &Pat<'_>, descr: &str, no_fields: bool) {
1498 let sess = self.tcx.sess;
1499 let sm = sess.source_map();
1500 let sp_brace = sm.end_point(pat.span);
1501 let sp_comma = sm.end_point(pat.span.with_hi(sp_brace.hi()));
1502 let sugg = if no_fields || sp_brace != sp_comma { ".. }" } else { ", .. }" };
1504 let mut err = struct_span_err!(
1508 "`..` required with {descr} marked as non-exhaustive",
1510 err.span_suggestion_verbose(
1512 "add `..` at the end of the field list to ignore all other fields",
1514 Applicability::MachineApplicable,
1519 fn error_field_already_bound(&self, span: Span, ident: Ident, other_field: Span) {
1524 "field `{}` bound multiple times in the pattern",
1527 .span_label(span, format!("multiple uses of `{ident}` in pattern"))
1528 .span_label(other_field, format!("first use of `{ident}`"))
1532 fn error_inexistent_fields(
1535 inexistent_fields: &[&hir::PatField<'tcx>],
1536 unmentioned_fields: &mut Vec<(&'tcx ty::FieldDef, Ident)>,
1537 variant: &ty::VariantDef,
1538 substs: &'tcx ty::List<ty::subst::GenericArg<'tcx>>,
1539 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1541 let (field_names, t, plural) = if inexistent_fields.len() == 1 {
1542 (format!("a field named `{}`", inexistent_fields[0].ident), "this", "")
1549 .map(|field| format!("`{}`", field.ident))
1550 .collect::<Vec<String>>()
1557 let spans = inexistent_fields.iter().map(|field| field.ident.span).collect::<Vec<_>>();
1558 let mut err = struct_span_err!(
1562 "{} `{}` does not have {}",
1564 tcx.def_path_str(variant.def_id),
1567 if let Some(pat_field) = inexistent_fields.last() {
1569 pat_field.ident.span,
1571 "{} `{}` does not have {} field{}",
1573 tcx.def_path_str(variant.def_id),
1579 if unmentioned_fields.len() == 1 {
1581 unmentioned_fields.iter().map(|(_, field)| field.name).collect::<Vec<_>>();
1582 let suggested_name = find_best_match_for_name(&input, pat_field.ident.name, None);
1583 if let Some(suggested_name) = suggested_name {
1584 err.span_suggestion(
1585 pat_field.ident.span,
1586 "a field with a similar name exists",
1588 Applicability::MaybeIncorrect,
1591 // When we have a tuple struct used with struct we don't want to suggest using
1592 // the (valid) struct syntax with numeric field names. Instead we want to
1593 // suggest the expected syntax. We infer that this is the case by parsing the
1594 // `Ident` into an unsized integer. The suggestion will be emitted elsewhere in
1595 // `smart_resolve_context_dependent_help`.
1596 if suggested_name.to_ident_string().parse::<usize>().is_err() {
1597 // We don't want to throw `E0027` in case we have thrown `E0026` for them.
1598 unmentioned_fields.retain(|&(_, x)| x.name != suggested_name);
1600 } else if inexistent_fields.len() == 1 {
1601 match pat_field.pat.kind {
1603 if !self.can_coerce(
1604 self.typeck_results.borrow().expr_ty(expr),
1606 unmentioned_fields[0].1.span,
1607 unmentioned_fields[0].0,
1612 let unmentioned_field = unmentioned_fields[0].1.name;
1613 err.span_suggestion_short(
1614 pat_field.ident.span,
1616 "`{}` has a field named `{}`",
1617 tcx.def_path_str(variant.def_id),
1620 unmentioned_field.to_string(),
1621 Applicability::MaybeIncorrect,
1628 if tcx.sess.teach(&err.get_code().unwrap()) {
1630 "This error indicates that a struct pattern attempted to \
1631 extract a non-existent field from a struct. Struct fields \
1632 are identified by the name used before the colon : so struct \
1633 patterns should resemble the declaration of the struct type \
1635 If you are using shorthand field patterns but want to refer \
1636 to the struct field by a different name, you should rename \
1643 fn error_tuple_variant_as_struct_pat(
1646 fields: &'tcx [hir::PatField<'tcx>],
1647 variant: &ty::VariantDef,
1648 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
1649 if let (CtorKind::Fn, PatKind::Struct(qpath, ..)) = (variant.ctor_kind, &pat.kind) {
1650 let path = rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1651 s.print_qpath(qpath, false)
1653 let mut err = struct_span_err!(
1657 "tuple variant `{}` written as struct variant",
1660 let (sugg, appl) = if fields.len() == variant.fields.len() {
1662 self.get_suggested_tuple_struct_pattern(fields, variant),
1663 Applicability::MachineApplicable,
1667 variant.fields.iter().map(|_| "_").collect::<Vec<&str>>().join(", "),
1668 Applicability::MaybeIncorrect,
1671 err.span_suggestion_verbose(
1672 qpath.span().shrink_to_hi().to(pat.span.shrink_to_hi()),
1673 "use the tuple variant pattern syntax instead",
1674 format!("({})", sugg),
1682 fn get_suggested_tuple_struct_pattern(
1684 fields: &[hir::PatField<'_>],
1685 variant: &VariantDef,
1687 let variant_field_idents =
1688 variant.fields.iter().map(|f| f.ident(self.tcx)).collect::<Vec<Ident>>();
1692 match self.tcx.sess.source_map().span_to_snippet(field.pat.span) {
1694 // Field names are numbers, but numbers
1695 // are not valid identifiers
1696 if variant_field_idents.contains(&field.ident) {
1702 Err(_) => rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| {
1703 s.print_pat(field.pat)
1707 .collect::<Vec<String>>()
1711 /// Returns a diagnostic reporting a struct pattern which is missing an `..` due to
1712 /// inaccessible fields.
1715 /// error: pattern requires `..` due to inaccessible fields
1716 /// --> src/main.rs:10:9
1718 /// LL | let foo::Foo {} = foo::Foo::default();
1721 /// help: add a `..`
1723 /// LL | let foo::Foo { .. } = foo::Foo::default();
1726 fn error_no_accessible_fields(
1729 fields: &'tcx [hir::PatField<'tcx>],
1730 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1734 .struct_span_err(pat.span, "pattern requires `..` due to inaccessible fields");
1736 if let Some(field) = fields.last() {
1737 err.span_suggestion_verbose(
1738 field.span.shrink_to_hi(),
1739 "ignore the inaccessible and unused fields",
1741 Applicability::MachineApplicable,
1744 let qpath_span = if let PatKind::Struct(qpath, ..) = &pat.kind {
1747 bug!("`error_no_accessible_fields` called on non-struct pattern");
1750 // Shrink the span to exclude the `foo:Foo` in `foo::Foo { }`.
1751 let span = pat.span.with_lo(qpath_span.shrink_to_hi().hi());
1752 err.span_suggestion_verbose(
1754 "ignore the inaccessible and unused fields",
1756 Applicability::MachineApplicable,
1762 /// Report that a pattern for a `#[non_exhaustive]` struct marked with `non_exhaustive_omitted_patterns`
1763 /// is not exhaustive enough.
1765 /// Nb: the partner lint for enums lives in `compiler/rustc_mir_build/src/thir/pattern/usefulness.rs`.
1766 fn lint_non_exhaustive_omitted_patterns(
1769 unmentioned_fields: &[(&ty::FieldDef, Ident)],
1772 fn joined_uncovered_patterns(witnesses: &[&Ident]) -> String {
1773 const LIMIT: usize = 3;
1776 [witness] => format!("`{}`", witness),
1777 [head @ .., tail] if head.len() < LIMIT => {
1778 let head: Vec<_> = head.iter().map(<_>::to_string).collect();
1779 format!("`{}` and `{}`", head.join("`, `"), tail)
1782 let (head, tail) = witnesses.split_at(LIMIT);
1783 let head: Vec<_> = head.iter().map(<_>::to_string).collect();
1784 format!("`{}` and {} more", head.join("`, `"), tail.len())
1788 let joined_patterns = joined_uncovered_patterns(
1789 &unmentioned_fields.iter().map(|(_, i)| i).collect::<Vec<_>>(),
1792 self.tcx.struct_span_lint_hir(NON_EXHAUSTIVE_OMITTED_PATTERNS, pat.hir_id, pat.span, "some fields are not explicitly listed", |lint| {
1793 lint.span_label(pat.span, format!("field{} {} not listed", rustc_errors::pluralize!(unmentioned_fields.len()), joined_patterns));
1795 "ensure that all fields are mentioned explicitly by adding the suggested fields",
1798 "the pattern is of type `{}` and the `non_exhaustive_omitted_patterns` attribute was found",
1806 /// Returns a diagnostic reporting a struct pattern which does not mention some fields.
1809 /// error[E0027]: pattern does not mention field `bar`
1810 /// --> src/main.rs:15:9
1812 /// LL | let foo::Foo {} = foo::Foo::new();
1813 /// | ^^^^^^^^^^^ missing field `bar`
1815 fn error_unmentioned_fields(
1818 unmentioned_fields: &[(&ty::FieldDef, Ident)],
1819 have_inaccessible_fields: bool,
1820 fields: &'tcx [hir::PatField<'tcx>],
1821 ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
1822 let inaccessible = if have_inaccessible_fields { " and inaccessible fields" } else { "" };
1823 let field_names = if unmentioned_fields.len() == 1 {
1824 format!("field `{}`{}", unmentioned_fields[0].1, inaccessible)
1826 let fields = unmentioned_fields
1828 .map(|(_, name)| format!("`{}`", name))
1829 .collect::<Vec<String>>()
1831 format!("fields {}{}", fields, inaccessible)
1833 let mut err = struct_span_err!(
1837 "pattern does not mention {}",
1840 err.span_label(pat.span, format!("missing {}", field_names));
1841 let len = unmentioned_fields.len();
1842 let (prefix, postfix, sp) = match fields {
1843 [] => match &pat.kind {
1844 PatKind::Struct(path, [], false) => {
1845 (" { ", " }", path.span().shrink_to_hi().until(pat.span.shrink_to_hi()))
1850 // Account for last field having a trailing comma or parse recovery at the tail of
1851 // the pattern to avoid invalid suggestion (#78511).
1852 let tail = field.span.shrink_to_hi().with_hi(pat.span.hi());
1854 PatKind::Struct(..) => (", ", " }", tail),
1859 err.span_suggestion(
1862 "include the missing field{} in the pattern{}",
1864 if have_inaccessible_fields { " and ignore the inaccessible fields" } else { "" }
1871 .map(|(_, name)| name.to_string())
1872 .collect::<Vec<_>>()
1874 if have_inaccessible_fields { ", .." } else { "" },
1877 Applicability::MachineApplicable,
1879 err.span_suggestion(
1882 "if you don't care about {these} missing field{s}, you can explicitly ignore {them}",
1883 these = pluralize!("this", len),
1884 s = pluralize!(len),
1885 them = if len == 1 { "it" } else { "them" },
1887 format!("{}..{}", prefix, postfix),
1888 Applicability::MachineApplicable,
1896 inner: &'tcx Pat<'tcx>,
1898 def_bm: BindingMode,
1902 let (box_ty, inner_ty) = if self.check_dereferenceable(span, expected, inner) {
1903 // Here, `demand::subtype` is good enough, but I don't
1904 // think any errors can be introduced by using `demand::eqtype`.
1905 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1906 kind: TypeVariableOriginKind::TypeInference,
1909 let box_ty = tcx.mk_box(inner_ty);
1910 self.demand_eqtype_pat(span, expected, box_ty, ti);
1913 let err = tcx.ty_error();
1916 self.check_pat(inner, inner_ty, def_bm, ti);
1920 // Precondition: Pat is Ref(inner)
1923 pat: &'tcx Pat<'tcx>,
1924 inner: &'tcx Pat<'tcx>,
1925 mutbl: hir::Mutability,
1927 def_bm: BindingMode,
1931 let expected = self.shallow_resolve(expected);
1932 let (rptr_ty, inner_ty) = if self.check_dereferenceable(pat.span, expected, inner) {
1933 // `demand::subtype` would be good enough, but using `eqtype` turns
1934 // out to be equally general. See (note_1) for details.
1936 // Take region, inner-type from expected type if we can,
1937 // to avoid creating needless variables. This also helps with
1938 // the bad interactions of the given hack detailed in (note_1).
1939 debug!("check_pat_ref: expected={:?}", expected);
1940 match *expected.kind() {
1941 ty::Ref(_, r_ty, r_mutbl) if r_mutbl == mutbl => (expected, r_ty),
1943 let inner_ty = self.next_ty_var(TypeVariableOrigin {
1944 kind: TypeVariableOriginKind::TypeInference,
1947 let rptr_ty = self.new_ref_ty(pat.span, mutbl, inner_ty);
1948 debug!("check_pat_ref: demanding {:?} = {:?}", expected, rptr_ty);
1949 let err = self.demand_eqtype_pat_diag(pat.span, expected, rptr_ty, ti);
1951 // Look for a case like `fn foo(&foo: u32)` and suggest
1952 // `fn foo(foo: &u32)`
1953 if let Some(mut err) = err {
1954 self.borrow_pat_suggestion(&mut err, pat);
1961 let err = tcx.ty_error();
1964 self.check_pat(inner, inner_ty, def_bm, ti);
1968 /// Create a reference type with a fresh region variable.
1969 fn new_ref_ty(&self, span: Span, mutbl: hir::Mutability, ty: Ty<'tcx>) -> Ty<'tcx> {
1970 let region = self.next_region_var(infer::PatternRegion(span));
1971 let mt = ty::TypeAndMut { ty, mutbl };
1972 self.tcx.mk_ref(region, mt)
1975 /// Type check a slice pattern.
1977 /// Syntactically, these look like `[pat_0, ..., pat_n]`.
1978 /// Semantically, we are type checking a pattern with structure:
1979 /// ```ignore (not-rust)
1980 /// [before_0, ..., before_n, (slice, after_0, ... after_n)?]
1982 /// The type of `slice`, if it is present, depends on the `expected` type.
1983 /// If `slice` is missing, then so is `after_i`.
1984 /// If `slice` is present, it can still represent 0 elements.
1988 before: &'tcx [Pat<'tcx>],
1989 slice: Option<&'tcx Pat<'tcx>>,
1990 after: &'tcx [Pat<'tcx>],
1992 def_bm: BindingMode,
1995 let expected = self.structurally_resolved_type(span, expected);
1996 let (element_ty, opt_slice_ty, inferred) = match *expected.kind() {
1997 // An array, so we might have something like `let [a, b, c] = [0, 1, 2];`.
1998 ty::Array(element_ty, len) => {
1999 let min = before.len() as u64 + after.len() as u64;
2000 let (opt_slice_ty, expected) =
2001 self.check_array_pat_len(span, element_ty, expected, slice, len, min);
2002 // `opt_slice_ty.is_none()` => `slice.is_none()`.
2003 // Note, though, that opt_slice_ty could be `Some(error_ty)`.
2004 assert!(opt_slice_ty.is_some() || slice.is_none());
2005 (element_ty, opt_slice_ty, expected)
2007 ty::Slice(element_ty) => (element_ty, Some(expected), expected),
2008 // The expected type must be an array or slice, but was neither, so error.
2010 if !expected.references_error() {
2011 self.error_expected_array_or_slice(span, expected, ti);
2013 let err = self.tcx.ty_error();
2014 (err, Some(err), err)
2018 // Type check all the patterns before `slice`.
2020 self.check_pat(elt, element_ty, def_bm, ti);
2022 // Type check the `slice`, if present, against its expected type.
2023 if let Some(slice) = slice {
2024 self.check_pat(slice, opt_slice_ty.unwrap(), def_bm, ti);
2026 // Type check the elements after `slice`, if present.
2028 self.check_pat(elt, element_ty, def_bm, ti);
2033 /// Type check the length of an array pattern.
2035 /// Returns both the type of the variable length pattern (or `None`), and the potentially
2036 /// inferred array type. We only return `None` for the slice type if `slice.is_none()`.
2037 fn check_array_pat_len(
2040 element_ty: Ty<'tcx>,
2042 slice: Option<&'tcx Pat<'tcx>>,
2043 len: ty::Const<'tcx>,
2045 ) -> (Option<Ty<'tcx>>, Ty<'tcx>) {
2046 if let Some(len) = len.try_eval_usize(self.tcx, self.param_env) {
2047 // Now we know the length...
2048 if slice.is_none() {
2049 // ...and since there is no variable-length pattern,
2050 // we require an exact match between the number of elements
2051 // in the array pattern and as provided by the matched type.
2053 return (None, arr_ty);
2056 self.error_scrutinee_inconsistent_length(span, min_len, len);
2057 } else if let Some(pat_len) = len.checked_sub(min_len) {
2058 // The variable-length pattern was there,
2059 // so it has an array type with the remaining elements left as its size...
2060 return (Some(self.tcx.mk_array(element_ty, pat_len)), arr_ty);
2062 // ...however, in this case, there were no remaining elements.
2063 // That is, the slice pattern requires more than the array type offers.
2064 self.error_scrutinee_with_rest_inconsistent_length(span, min_len, len);
2066 } else if slice.is_none() {
2067 // We have a pattern with a fixed length,
2068 // which we can use to infer the length of the array.
2069 let updated_arr_ty = self.tcx.mk_array(element_ty, min_len);
2070 self.demand_eqtype(span, updated_arr_ty, arr_ty);
2071 return (None, updated_arr_ty);
2073 // We have a variable-length pattern and don't know the array length.
2074 // This happens if we have e.g.,
2075 // `let [a, b, ..] = arr` where `arr: [T; N]` where `const N: usize`.
2076 self.error_scrutinee_unfixed_length(span);
2079 // If we get here, we must have emitted an error.
2080 (Some(self.tcx.ty_error()), arr_ty)
2083 fn error_scrutinee_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
2088 "pattern requires {} element{} but array has {}",
2090 pluralize!(min_len),
2093 .span_label(span, format!("expected {} element{}", size, pluralize!(size)))
2097 fn error_scrutinee_with_rest_inconsistent_length(&self, span: Span, min_len: u64, size: u64) {
2102 "pattern requires at least {} element{} but array has {}",
2104 pluralize!(min_len),
2109 format!("pattern cannot match array of {} element{}", size, pluralize!(size),),
2114 fn error_scrutinee_unfixed_length(&self, span: Span) {
2119 "cannot pattern-match on an array without a fixed length",
2124 fn error_expected_array_or_slice(&self, span: Span, expected_ty: Ty<'tcx>, ti: TopInfo<'tcx>) {
2125 let mut err = struct_span_err!(
2129 "expected an array or slice, found `{expected_ty}`"
2131 if let ty::Ref(_, ty, _) = expected_ty.kind()
2132 && let ty::Array(..) | ty::Slice(..) = ty.kind()
2134 err.help("the semantics of slice patterns changed recently; see issue #62254");
2135 } else if Autoderef::new(&self.infcx, self.param_env, self.body_id, span, expected_ty, span)
2136 .any(|(ty, _)| matches!(ty.kind(), ty::Slice(..) | ty::Array(..)))
2137 && let (Some(span), true) = (ti.span, ti.origin_expr)
2138 && let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span)
2140 let ty = self.resolve_vars_if_possible(ti.expected);
2141 let is_slice_or_array_or_vector = self.is_slice_or_array_or_vector(&mut err, snippet.clone(), ty);
2142 match is_slice_or_array_or_vector.1.kind() {
2144 if self.tcx.is_diagnostic_item(sym::Option, adt_def.did())
2145 || self.tcx.is_diagnostic_item(sym::Result, adt_def.did()) =>
2147 // Slicing won't work here, but `.as_deref()` might (issue #91328).
2148 err.span_suggestion(
2150 "consider using `as_deref` here",
2151 format!("{snippet}.as_deref()"),
2152 Applicability::MaybeIncorrect,
2157 if is_slice_or_array_or_vector.0 {
2158 err.span_suggestion(
2160 "consider slicing here",
2161 format!("{snippet}[..]"),
2162 Applicability::MachineApplicable,
2166 err.span_label(span, format!("pattern cannot match with input type `{expected_ty}`"));
2170 fn is_slice_or_array_or_vector(
2172 err: &mut Diagnostic,
2175 ) -> (bool, Ty<'tcx>) {
2177 ty::Adt(adt_def, _) if self.tcx.is_diagnostic_item(sym::Vec, adt_def.did()) => {
2180 ty::Ref(_, ty, _) => self.is_slice_or_array_or_vector(err, snippet, *ty),
2181 ty::Slice(..) | ty::Array(..) => (true, ty),